Optical disk recording/reproducing apparatus with synchronized data writing

ABSTRACT

An optical disc recording/reproducing apparatus for recording and reproducing data using an optical disc as the recording medium, wherein use is made of an optical disc (1) having pit regions (2a) with servo pits and data regions (2a) on which data will be written, that are alternately provided along the circumferential direction, reference clocks are formed in synchronism with said servo pits, and a laser diode (21) is driven by pulses in synchronism with the reference clocks to write or erase the data, thus enabling the life of the laser diode to be lengthened and the disc capacity to be effectively utilized.

TECHNICAL FIELD

This invention relates to an optical disk recording/reproducingapparatus wherein an optical disk is used as the recording medium toeffect data recording and reproduction.

BACKGROUND

An opto-magnetic disk has been known as the large capacity recordingmedium permitting data re-writing. The data writing, reading and erasureto and from the opto-magnetic disk are usually performed with the use ofa laser beam emitted by a laser diode. Heretofore, at the time of datawriting or erasure, the laser diode remains energized during the periodsother than the periods during which the laser beam irradiation isactually required, with the result that the life of the laser diode isshort and the demanded guarantee time cannot be satisfied.

The tracks on the opto-magnetic disk are each divided into a pluralityof sections, each of which is provided with a gap region for absorbingtemporary errors, with the data being recorded in synchronism with eachsector as one unit to effect data management or control on the sectorbasis.

With the opto-magnetic disk apparatus in which the opto-magnetic disk isemployed as the recording medium and the data are recorded and/orreproduced by a laser diode, problems are presented as to the life ofthe laser diode and the reduction in the effective disk capacity, withthe gap region provided in each track sector on the opto-magnetic diskrepresenting an ineffective recording region.

It is therefore an object of the present invention to provide an opticaldisk recording/reproducing apparatus enabling the life of the laserdiode to be lengthened and the disk capacity to be effectively utilized.

SUMMARY OF THE INVENTION

For accomplishing the above object, the present invention is applied toan opto-magnetic disk apparatus employing, for example, an opto-magneticdisk as the recording medium, and the optical disk recording/reproducingapparatus according to the present invention is characterized in that anopto-magnetic disk having pit regions with servo pits and data regionson which data will be written, that are alternately provided along thecircumferential direction, is revolved at a constant angular velocity,reference clocks are formed in synchronism with said pits on the basisof the detection output obtained upon detecting said servo pits, and inthat a laser diode is driven by pulses in synchronism with saidreference clocks to write or erase data to or from said data region.

According to the present invention, the laser diode is driven by pulsesat the timing of the reference clocks synchronized with the servo pitsin the pit region of the opto-magnetic disk so that the datasynchronized for the disk in its entirety may be written in each dataregion. The data thus written are erased on the bit-by-bit basis bydriving the laser diode with pulses at the timing of the aforementionedreference clocks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing recording patterns of theopto-magnetic disk employed in an embodiment of the present invention;

FIG. 2 is a schematic view showing the constitution of each track in theabove embodiment;

FIG. 3 is a schematic view showing the construction of each pit region;

FIG. 4 is a schematic view showing the arrangement of the pits existingalong the radial direction of the disk;

FIG. 5 is a block diagram showing the,, overall construction of anembodiment of the opto-magnetic disk apparatus according to the presentinvention;

FIG. 6 is a circuit diagram showing a typical construction of a laserdrive circuit in the above embodiment;

FIG. 7 is a timing chart for understanding the operation of theaforementioned laser drive circuit;

FIG. 8 is a circuit diagram showing another typical construction of thelaser drive circuit in the above embodiment;

FIG. 9 is a timing chart for understanding the operation of the laserdrive circuit shown in FIG. 8;

FIG. 10 is a block diagram showing the overall construction of amodified embodiment of the opto-magnetic disk according to the presentinvention;

FIG. 11 is a circuit diagram showing a further typical construction ofthe laser drive circuit in the above modified embodiment; and

FIG. 12 is a timing chart for understanding the operation of the laserdrive circuit shown in FIG. 11.

BEST MODE FOR PRACTICE OF THE INVENTION

An embodiment of an opto-magnetic disk apparatus to which the presentinvention is applied will be explained by referring to the drawings.

Referring to FIG. 1, wherein the recording pattern of the opto-magneticdisk employed in the present embodiment is illustrated, an opto-magneticdisk 1 has the diameter of, for example, about 13 cm, and the storagecapacity of not less than 300M bytes on one side. The disk 1 is rotatedwith a constant angular velocity and tracks 2 are formed concentricallyat the rate of one track per each disk revolution for recording thedata. About 18,000 to 20,000 tracks are formed on one side, with eachtrack being divided into, for example, 32 sectors.

As shown to an enlarged scale in FIG. 2, each track is composed of pitregions 2a having servo pits and data regions 2b on which data will bewritten, these regions 2a and 2b being alternately provided along thecircumferential direction of the disk. Each pit region 2a has a lengthof 2 bytes and each data region 2b has a length of 16 bytes, whenmeasured in terms of the numbers of bits.

Three pits P_(A), P_(B) and P_(C) are formed in each pit region 2a, asshown in FIG. 3. The pits P_(A) and P_(B) are formed with a verticaloffset on both sides of a centerline of the track formed in the disk 1,while the pit P_(C) is formed on the centerline of the track. These pitP_(A), P_(B) and P_(C) are about 0.5 to 1.0 micron in diameter, with theactual length L of the pit region 2a being 19 to 30 microns.

FIG. 4 shows the disposition of the pits P_(A), P_(B) and P_(C) alongthe radial direction of the disk as indicated by the arrow mark inFIG. 1. Thus the pits P_(B) and P_(C) are arranged in straight lines,whereas the pits P_(A) are offset lengthwise of the track by groups of16 consecutive pits. The offset disposition of the pits P_(A) by groupsof 16 consecutive pits is utilized to effect traverse counting as laterdescribed in order for the optical pickup to find the track number ofthe track being scanned. The pits P_(A) are sampled by the samplingpulse SP₁ or the sampling pulse SP₂ and the pits P_(B) and P_(C) aresampled by the sampling pulses SP₃ and SP₅, respectively, while themirror surface regions between the pits P_(B) and P_(C) are sampled bythe sampling pulses SP₄ so as to be utilized for various servo controloperations and clock generation as later described.

Referring to FIG. 5, wherein the overall construction of theopto-magnetic disk apparatus of the present invention is illustrated,data D₁ to be recorded are supplied to an input terminal 11 from, forexample, a computer through an interface (I/O). These data D₁ aresupplied to a modulating circuit 12 where they undergo modulationincluding bit conversion before being supplied to a laser drive circuit13. Write, read or erasure mode control signals are supplied from theinterface to the laser drive circuit 13 via the "Control Signal" Bus.The drive circuit 13 which, responsive to these control signals,operates to supply signals for driving the laser diode 21 of the opticalpickup 20, in order to supply drive pulse signals timed in accordancewith the channel clocks CCK to the laser diode 21 as the referenceclocks during data recording and erasure, while also supplying highfrequency drive signals to the laser diode 21 during data reading.

The optical pickup 20 includes, in addition to the laser diode 21, aphotodiode 22 and photodetectors 23 and 24, each divided into foursections. The photodiode 22 is designed to sense the intensity of thelaser light emitted by the laser diode 21. The photodetectors 23, 24 aredisigned to sense the laser light reflected by the opto-magnetic disk 1,one of the photodetectors sensing the positive direction component ofthe Kerr rotation angle and the other sensing its negative directioncomponent.

An electric motor 14 is controlled by a motor servo circuit 15 by, forexample, a phase locked loop (PLL) to cause the disk 1 to the rotatedaccurately at a prescribed velocity (angular velocity).

The laser light supplied from the laser diode 21 is irradiated on theopto-magnetic disk 1, while being supplied to the photodiode 22. Theoutput of the photodiode 22 proportionate to the laser light intensityis supplied to a sample and hold circuit (S/H) 17 through a d.c.amplifier 16. The S/H circuit 17 performs a sample and hold operation inaccordance with the sampling pulses SP₄ (see FIG. 4) and the outputtherefrom is supplied through an APC amplifier 18 to the laser drivecircuit 13 as the automatic power control or APC signals. This causesthe intensity of the laser light supplied from the laser diode 21 to bemaintained at a prescribed value.

The laser light reflected by the disk 1 is supplied via a lightdetector, not shown, to photo-detectors 23 and 24 of the optical pickup20, the output signals of which are supplied to a pre-amplifier 31. Fromthe pre-amplifier 31, a light detection signal S_(A) or the sum of theoutputs from the respective light receiving regions of thephoto-detectors 23 and 24 (S_(A) =A+B+C+D+A'+B'+C'+D') (including thed.c. components) are directly supplied to a focus servo circuit 32, anda light detection signal S_(B) composed of the outputs from therespective light receiving regions of the photodetectors 23 and 24(SB=(AC-BC)+(A'C'-B'D')) are also supplied to the focus servo circuit 32through the S/H circuit 33 adapted for performing the sample and holdoperations in dependence upon the sampling pulses SP₄. Focus servocontrol signals produced in the focus servo circuit 32 on the basis ofthe respective signals S_(A) and S_(B) are supplied for focus control tothe optical pickup 20.

The light detection signal SC from the pre-amplifier 31 (S_(C)=A+B+C+D+A'+B'+C'+D') are supplied to a peak position detection circut41, S/H circuit 51, 52 and 53 and to a sampling clamp circuit 61. Thelight detection signal S_(C) is the detection signal of patterns ofprojections and recesses in the pit region 2a of the disk 1. The peakposition of the light detection signal S_(C) is detected in the peakposition detection circuit 41, while the pit pattern having an intervalproper to the interval between the pits P_(B) and P_(C) on the disk 1are detected in a proper pattern detection circuit 42 to detect the pitsP_(C). The detected output is supplied via a delay circuit 43 to a pulsegenerator 44. Channel clocks CCK are generated in the pulse generator 44as the reference clocks synchronized with the pits P_(C) on the basis ofthe detection output obtained in the proper pattern detecting circuit42. In the pulse generator 44, byte clocks BYC, servo byte clocks SBCand sampling pulses SP₁, SP₂, SP₃, SP₄ and SP₅ are formed and outputted,as shown in FIG. 4. Although not shown, the channel clocks CCK aresupplied to all of the circuit blocks The sample pulses SP₁, SP₂ and SP₃are supplied to an S/H circuit 51, S/H circuit 52 and to an S/H circuit53, respectively. The sampling pulses SP₄ are supplied to theaforementioned S/H circuit 17 and 33 while being also supplied to thesampling clamp circuit 61 and 62. It is noted that the sampling pulsesSP₅ are used for detecting the moving direction, for example, of theoptical pickup 20. The peak position detection circuit 41 and the properpattern detection circuit 42 are also supplied with gate pulses from thepulse generator 44.

In the S/H circuits, sample and hold operations are performed of thesupplied light detection signal by the aforementioned sampling pulsesSP₁, SP₂ and SP₃. The signal levels of the outputs from the S/H circuits51 and 52 are compared in a comparator 54. The comparator output isinverted every 16 tracks as the result of the aforementioned radialdisposition of the pits P_(A) on the disk 1, and is supplied as thetraverse count signal to a tracking servo/seek circuit 55, while alsobeing supplied to a multiplexer 56. From this multiplexer 56, the signalfrom the S/H circuit 51 or from the S/H circuit 52, whichever is higherin signal level, is selectively outputted and supplied to a subtractor57. A difference signal between the signal from the multiplexor 56 andthat from the S/H circuit 53 is formed and supplied therefrom as thetracking error signal to the aforementioned tracking servo/seek circuit55. The tracking servo/seek circuit 55 performs tracking and feedcontrol operations for the optical pickup 20.

The aforemntioned light detection signal S_(C) and a light detectionsignal S_(D) (S_(D) =(A+B+C+D)-(A'+B'+C'+D')) are supplied from thepre-amplifier 31 to the sampling clamp circuits 61 and 62, respectively.The light detection signal S_(C) is the detection signal of patterns ofprojections and recesses in the pit region 2a of the disk 1, asdiscussed above. The light detection signal S_(D) is the detectionsignal of data written in the data region 2b of the disk 1. In thesampling clamps 61 and 62, the respective signals are clamped by thesampling pulses SP₄ before being supplied to the multiplexor 63. Theswitching selecting operation of the multiplexor 63 is controlled bycontrol signals from a sync detection/address decoding circuit 64.Assuming that, for example, the light detection signal S_(C) is suppliedby way of the sampling clamp circuit 61 and the multiplexor 63 to ananalog to digital (A/D) converter 65 so as to be converted into thedigital value which is then supplied to a demodulator 66, the outputfrom the demodulator 66 is supplied to a sync detect/address decodecircuit 64 where the sync signals are detected and the addressinformation is decoded. When the address information of the datasupplied through an interface from a computer so as to be read coincideswith the actual address, the multiplexor 63 is switched, so that thelight detection signal S_(D) for the data region 2b is supplied to theA/D converter 65 and to the demodulator 66 to supply the data D₀ thathave undergone demodulation including bit conversion from the outputterminal 67. These data D₀ are supplied through an interface to acomputer. During data writing, control signals are supplied from thesync detect/address decode circuit 64 to a modulator 12 and, inaccordance with these control signals, the data to be written aretransmitted from the demodulator 12 to the laser drive circuit 13.

FIG. 6 illustrates a typical construction of the drive control systemfor the laser diode 21.

Referring to FIG. 6, control pulses indicating the read operation aresupplied to a terminal 71, while control pulses indicating the write orerasure operations are supplied to the terminal 75.

The terminal 75 is connected via transistor Q₁ to a base of a transistorQ₂. The transistor Q₂ is connected in a collector and emitter commonconfiguration to a transistor Q₃. The collector of the transistor Q₃ isconnected to a resistor R₁ and to a base of the transistor Q₄. Theemitter of the transistor Q₄ is connected via diode 72 to the base ofthe transistor Q₃. The aforementioned transistor Q₃ and Q₄ and the diode72 make up a ring oscillator. The transistors Q₃ and Q₅ have theiremitters connected in common to the collector of a transistor Q₆ used asa current source, while the emitter of the transistor Q₆ is connectedvia resistor R₂ to a power source terminal 73. The base of thetransistor Q₅ is connected to a terminal 74 adapted to supply aprescribed base potential V_(BB).

The terminal 75 is connected via transistor Q₇ to the base of atransistor Q₈. The collector of the transistor Q₈ is connected the laserdiode 21, while being also connected to the collector of the transistorQ₅. A transistor Q₉ has its collector grounded via resistor R₃ and itsbase connected to the terminal 74. The transistors Q₈ and Q₉ have theiremitters connected in common to the collector of the current sourcetransistor Q₁₀, the emitter of which is connected via resistor R₄ to thepower source terminal 73.

The intensity of the laser light radiated from the laser diode 21 isdetected by a photodiode 22 which is connected to a resistor R₅ and to aswitching element 77 through an operational amplifier 76 adapted ford.c. amplification. The switching element 77 is connected to a capacitorC₁ and to an operational amplifier 78 acting as a high input impedancebuffer. The switching element 77 is supplied with the aforementionedsampling pulses SP₄ and performs a sampling operation of sampling theoutput of the photodiode 22 supplied via operational amplifier 76 by theaforementioned sampling pulses SP₄ and holding the sampled output in thecapacitor C₁. The output of the operational amplifier 78 is connectedvia resistor R₆ to the inverting inputs of the operational amplifiers 79and 80. A reference voltage V_(ref) is supplied to each of thenon-inverting inputs of the operational amplifiers 79 and 80, the oneoutput of which is connected to the base of the transistor Q₆ and theother output of which is connected to the base of the transistor Q₁₀.The inverting input of the operational amplifier 80 is connected viaresistor Q₇ to a terminal 81. To this terminal 81 are supplied controlsignals for switching the output of the laser diode 21 between the writeand erase modes.

In the above described drive control system for the laser diode 21, whenthe terminal 71 is at the low (L) level, the transistors Q₁ and Q₂ arekept in the OFF state, the ring oscillator formed by the transistors Q₃and Q₄ performing the high frequency oscillation with the frequency of,for example, about 100 to 500 MHz. As a result, the laser diode 21 issupplied via transistor Q₅ with a high frequency current having thecurrent i_(CSH) by the current source transistor Q₆ as the peak value,so as to be thereby driven into high frequency operation. With theterminal 71 in the high (H) level, the transistor Q₁ and Q₂ are kept intheir ON state, so that the current i_(CSH) by the transistor Q₆ flowsthrough the resistor R₁ via transistor Q₂, while the driving of thelaser diode 21 and the oscillation of the ring oscillator areterminated.

The driving of the laser diode 21 by the high frequency current of thelaser diode 21 is achieved with the control pulses going low during theread out operation being supplied to the terminal 71.

With the terminal 75 in the L level, the transistors Q₇ and Q₈ are keptin the OFF state, with the current i_(CSS) by the current sourcetransistor Q₁₀ not flowing through the laser diode 21 but flowing viatransistor Q₉ through the resistor R₃. With the terminal 75 in the Hlevel, the respective transistors Q₇ and Q₈ are turned on, with thecurrent i_(CSS) by the current source transistor Q₁₀ flowing viatransistor Q₈ through the laser diode 21. In the present embodiment,during the write mode, for example, control pulses associated with dataare supplied to the terminal 75 for driving the laser diode 21 withpulses in association with the data in order to effect data writing.

The operation of the drive control system of the laser diode 21 isexplained more specifically by referring to FIG. 7, wherein the waveformof the current i_(LD) supplied to the lasr diode 21 is shown. Thus thecurrent waveforms for the write-, erase-, read-out and stand-by modesare shown in FIGS. 7A, 7B, 7C and 7D, respectively.

With the write mode, the terminals 71 and 75 are kept in the L levelduring the period corresponding to the aforementioned pit region 2a, sothat, as shown in FIG. 7A, the laser diode 21 is driven by the highfrequency current. During the period correspondig to the data region 2b,the terminal 71 is kept in the H level and the data pulse associatedwith the write data are supplied to the terminal 75 for driving thelaser diode 21 with pulses in order to effect data writing. The writetiming, that is, the timing of the aforementioned data pulses, iscoincident with the channel clocks CCK formed on the basis of thedetection output of the pits P_(C).

It is noted that, during the period corresponding to the aforementionedpit region 2a, the laser diode 21 is driven necessarily by the highfrequency current in order to effect the read operation even when theoperating mode is other than the write mode.

With the erasure mode, the terminal 71 is kept at the H level during theperiod corresponding to the data region 2b and repetitive pulses aresupplied to the terminal 75 for driving the laser diode 21 by pulses toeffect data erasure, as shown in FIG. 7B. The timing of the erasureoperation, that is, that of the aforementioned repetitive pulses, isalso coincident with that of the channel clocks CCK, such that the datarecorded in the data region 2b are erased sequentially on the bit-by-bitbasis.

With the read-out mode, both the terminals 71 and 75 are maintained inthe L level during the periods corresponding to the pit region 2a anddata region 2b, that is, the totality of the pulse period, the laserdiode 21 being thus driven by the high frequency current as shown inFIG. 7C in order to effect data reading.

With the stand-by mode, the terminal 75 is maintained in the L-levelduring the period corresponding to the data region 2b to stop thedriving of the laser diode 21 in order to perform only the reading ofthe pit region 2a.

In any of the aforementioned operating modes, the bases of thetransistors Q₆ and Q₁₀ are controlled by automatic power control by theoperation of the APC circuit system including the photo-diode 22 inorder to maintain a prescribed output (light intensity) of the laserdiode 21. The control signal voltage applied to the terminal 81 is setto a value for the record mode different from one for the erase mode sothat a larger drive current will flow through the laser diode 21 duringthe erasure mode than during the record mode to provide for morereliable erasure operation.

By driving the laser diode 21 by pulses more efficiently during the datawrite and erasure modes, it becomes possible to extend the life of thelaser diode 21 while achieving the saving in power and reducing radiohindrances.

FIG. 8 illustrates a modified drive control system for the laser diode21. It is noted that parts or components corresponding to those shown inFIG. 6 are indicated in FIG. 8 by the same reference numerals and thecorresponding description is omitted.

In the present system, the terminal 91 supplied with control pulses isconnected via transistor Q₁₁ to bases of transistors Q₁₂ and Q₁₃, whilethe collector of the transistor Q₁₂ is grounded via resistor R₈. Thetransistor Q₁₄ has its collector connected to the laser diode 21 and itsbase to a terminal 92 supplied with a predetermined base voltage V_(BB).The emitters of the transistors Q₁₂ and Q₁₄ are connected in common tothe collector of the current source transistor Q₁₀. The base of thetransistor Q₁₀ is connected to a terminal 93 supplied with a controlsignal whereby the drive current caused to flow through the laser diode21 is switched between the record and erasure modes.

The collector of the transistor Q₁₅ is connected to the resistor R₉ andto the base of the transistor Q₁₆. The emitter of the transistor Q₁₆ isconnected via diode 94 to the base of the transistor Q₁₅. Thetransistors Q₁₅, Q₁₆ and the diode 94 constitute a ring oscillator. Thetransistor Q₁₇ has its collector connected to the laser diode 21 and itsbase connected to a terminal 95 supplying the prescribed base voltageV_(BB'). The transistors Q₁₅ and Q₁₇ have their emitters connected incommon to the collector of the transistior Q₁₃. The transistor Q₁₈ hasits collector connected to the laser diode 21 and its base to theterminal 92. The transistor Q₁₃ and Q₁₈ have their emitters connected incommon to the collector of the current source transistor Q₆.

The above described driving control system of the laser diode 21operates in the following manner.

With the terminal 91 at the L-level, the transistors Q₁₁, Q₁₂ and Q₁₃are turned off, while the transistors Q₁₄ and Q₁₅ are turned on.Therefore, the current i_(CSS) flowing through the transistor Q₁₄ andthe current i_(CSH) flowing through the transistor Q₁₈ are supplied tothe laser diode 21. Thus the drive current (i_(CSS) +i_(CSH)) issupplied to the laser diode 21, such that an automatic power control iscaused to occur both with the write and erasure modes by the APC signalssupplied from the APC circuit system to the base of the transistor Q₆.

With the terminal 91 at the H level, the transistors Q₁₁, Q₁₂ and Q₁₃are turned on, while the transistors Q₁₄ and Q₁₈ are turned off. Thetransistors Q₁₅ and Q₁₆ act as a ring oscillator to perform a highfrequency oscillation. As a result, the high frequency current havingthe current i_(CSH) by the current source transistor Q₆ as the peakvalue is supplied via transistors Q₁₃ and Q₁₇ to the laser diode 21which is thereby driven into high frequency operation. The current bythe transistor Q₁₀ flows to the resistor R₈ via transistor Q₁₂.

The operation of the drive control system for the laser diode 21 shownin FIG. 8 is explained more specificaly by referring to FIG. 9, whereinthe waveform of hte current i_(LD) supplied to the laser diode 21 isshown. Thus the current waveforms during the write-, erasure and readout modes are shown in FIGS. 9A, 9B and 9C, respectively.

During the write mode, data pulses associated with the write data aresupplied to the terminal 91 during the periods corresponding to the dataregion 2b, so that the laser diode 21 is driven by pulses, as shown inFIG. 9A, in order to effect data writing in the data region 2b. Duringthe time interval devoid of the aforementioned data pulses, with theterminal 91 being at the H-level, the transistors Q₁₅ and Q₁₆ act as aring oscillator to drive the laser diode 21 by the high frequencycurrent. This high frequency driving affords a so-called pre-heating forthe actual data write operation for assuring a smooth writing operation.

With the erasure mode operation, as shown in FIG. 9B, the laser diode 21is driven by the high frequency, at the same time that the erasurepulses having the prescribed repetitive pulse are supplied to theterminal 91 during the time period corresponding to the data region 2b,so that the laser diode 21 is driven by pulses to effect the erasure ofthe data region 2b.

With the read-out mode, the terminal 91 is maintained at an H-level, sothat, as shown in FIG. 9C, the laser diode 21 is driven by the highfrequency current to effect data reading. By reading the data in thismanner with the lasser diode 21 driven by the high frequency current, itbecomes possible to prevent the noise occurrence due to the return beamof the laser light irradiated on the opto-magnetic disk 1 whileextending the service life of the laser diode 21.

It is noted that, in the drive control system shown in FIG. 6, theoperation similar to that shown in FIG. 9 may be obtained when the basesof the transistors Q₂ and Q₃ are connected to each other for supplyingone-input control pulses.

FIG. 10 shows a modified embodiment of the opto-magnetic disk apparatusshown in FIG. 5. The apparatus shown herein includes control inputterminals 5, 6 and 7 supplied with an erasure mode signal S_(ER), awrite mode signal S_(WR) and a read mode signal S_(RE) through aninterface, respectively. The erasure mode signal S_(ER) and the writemode signals S_(WR) are supplied to the modulator 12 and the read modesignals are supplied from the control input terminal 7 through the NORgate 3 to the laser drive circuit 13 while also being supplied via ORgate 9 to the APC amplifier 18. It is noted that a delay compensationcircuit 10 is provided between the modulator 12 and the laser drivecircuit 13 and that the aforemntioned erasure mode signal S_(ER) andwrite mode signals S_(WR) are also supplied to this delay compensationcircuit 10 from the control input terminals 5 and 6, respectively

The laser drive control system of the present embodiment formed by theaforementioned laser drive circuit 13 and the APC amplifier 18 is shownmore specifically in FIG. 11 wherein the output terminal of theoperational amplifier 79 in the drive control system shown in FIG. 6 isconnected via switching circuit 82 to the base of the transistor Q₆,while the output terminal of the operational amplifier 80 is connectedvia switching circuit 83 to the base of the transistor Q₁₀. Theseswitching circuit 82 and 83 are connected to a terminal 84 adapted forsupplying a prescribed voltage, herein a voltage V_(EE) equal to thevoltage supplied to the power source terminal 73. The switching circuits82 and 83 are controlled and switched by a switching pulse P_(SW)supplied to the terminal 85 from the aforementioned OR gate 9. With theswitching pulse P_(SW) at the high (H) level, the outputs of theoperational amplifiers 79 and 80 are supplied to the bases of thetransistors Q₆ and Q₁₀ and, with the switching pulse P_(SW) at the low(L) level, the voltage V_(EE) at the terminal 84 is supplied to thebases of the transistors Q₆ and Q₁₀.

In the present embodiment, the operation of the modulator 12 and thedelay compensation circuit 10 is switched by the erasure mode signalsS_(ER) and the write mode signals S_(WR) supplied to the control inputterminals 5 and 6, such that, responsive to the data D₁ supplied to thesignal input terminal 11 during the write operating mode, data pulsestimed with the aforementioned channel clocks CCK are supplied from themodulator 12 via delay compensation circuit 10 to the terminal 75 of thelaser drive circuit 13, whereby, as hown in FIG. 12A, the laser diode 21is driven by pulses to write data on the data region 2b of theopto-magnetic disk 1. With the erasure mode operation, erasure pulsestimed with the aforementioned channel clocks CCK are supplied from themodulator 12 via delay compensation circuit 10 to the terminal 75 of thelaser drive circuit 13, whereby, as shown in FIG. 12B, the laser diode21 is driven by pulses to effect data erasure. For more reliableerasure, the delay compensation circuit 10 operates to provide theerasure pulse for the erasure mode having a larger pulse width W_(ER)than the pulse width W_(WR) of the write pulse for the write mode.

During the read mode, the terminals 71 and 75 are maintained at theL-level during the period corresponding to the pit region 2a and thedata region 2b, that is, the totality of the pulse period, for highfrequency driving of the laser diode 21 to read out data, as shown inFIG. 12C.

During the stand-by mode, the terminal 75 is maintained at the L-levelduring the period corresponding to the data region 2b, as shown in FIG.12D, to stop the driving of the laser diode 21 to perform only readingof the pit region 2a.

In the present drive control system, the switching pulse P_(SW) shown inFIG. 12E, that is, the pulse going high during the driving period of thelaser diode 21 corresponding to the pit region 2a and going low duringthe non-drive period of the laser diode 21 corresponding to the dataregion 2b, is supplied from the pulse generator 44 via OR gate 9 to theterminal 85. In this manner, during the drive period of the laser diode21, the output of the operational amplifier 79 is supplied to the baseof the transistor Q₆ to effect the automatic power control by the APCcircuit including the photodiode 22 to provide the constant output orlight intensity of the laser diode 21. During the non-drive period, thevoltage V_(EE) at the terminal 84 is supplied to the bases of thetransistors Q₆ and Q₁₀ so that these transistors are turned off toprevent the current from flowing thorugh resistors R₁ and R₃. When thecurrent is prevented in this manner from flowing through the resistorsR₁ and R.sub. 3 during the non-drive period, power consumption can bereduced to about one ninth that when using the drive control systemshown in FIG. 6, so that degradation of the circuit elements due to heatgeneration is also prevented.

Although the foregoing description has been made of the apparatusemploying the opto-magnetic disk as the recording medium, the technologydisclosed in the present invention is applicable to any erasablerecording media other than the opto-magnetic disk.

What is claimed is:
 1. An optical disk recording and reproducingapparatus comprising disk drive means for revolving an optical disk at aconstant angular velocity, said disk including pit regions having servopits and data regions on which data can be recorded, said pit and dataregions being alternately provided along the circumferential directionof the disk, an optical head including a laser diode emitting laserlight irradiating said optical disk, first detection means to detectlight reflected from said servo pits in said pit regions and lightreflected from said disk in said data regions, reference clock pulsegenerating means for forming reference clock pulses synchronized withsaid servo pits on said optical disk, said reference clock pulsegenerating means being connected to said first detection means andresponsive to an output therefrom obtained from detecting said servopits and for generating said reference clock pulses in response thereto,and a laser drive means connected to receive said reference clock pulsesfor driving said laser diode with pulses in synchronism with saidreference clock pulses while said laser diode is irradiating said dataregions, with data in said data regions of said optical disk beingerased by driving said laser diode with said pulses.
 2. An optical diskrecording and reproducing apparatus according to claim 1, includingmeans connected to receive said reference clock pulses for supplyingdrive pulses for data writing to said laser drive means in synchronismwith said reference clock pulses, whereby said laser diode is drivenwith said drive pulses to write data onto said data regions or to erasedata from said data regions by writing predetermined data.
 3. An opticaldisk recording and reproducing apparatus according to claim 2,characterized in that data are recorded on said data region by drivepulses synchronized with said reference clock pulses at the rate of onebit of data per pulse, with data being erased from said data region on abit-by-bit basis.
 4. An optical disk recording and reproducing apparatusaccording to claim 3, characterized in that said laser drive meanscauses the driving of said laser diode to be stopped during the intervalbetween said drive pulses for data erasure or data writing which drivesaid laser diode in synchronism with said reference clock pulses.
 5. Anoptical disk recording and reproducing apparatus according to claim 3,characterized in that said laser drive means includes means causing anextremely small current to flow through said laser diode during theinterval between said drive pulses for data erasure or data writingwhich drive said laser diode in synchronism with said reference clocks.6. An optical disk recording and reproducing apparatus according toclaim 5, characterized in that said extremely small current is suppliedto said laser drive means in the form of high frequency current.
 7. Anoptical disk recording and reproducing apparatus according to claim 6,including reading means connected to said head for reading out data fromsaid optical disk, said reading means including for driving said laserdiode with said high frequency current during operation of said readingmeans, whereby data recorded on said optical disk are read-out inresponse to the laser output of said laser diode.
 8. An optical diskrecording and reproducing apparatus according to claim 1, including anautomatic power control circuit provided in said laser drive means, saidautomatic power control means including sample and hold means connectedto receive said reference clock pulses, and control means connected tosaid sample and hold means for controlling the output level of saidlaser diode at a constant power level by power control signals formed byoperation of said sample and hold means in response to said referenceclock pulses.
 9. An optical disk recording and reproducing apparatusaccording to claim 8, characterized in that said automatic power controlcircuit includes switching means for interrupting the operating currentof said laser drive circuit during periods when the data is not beingwritten to or read or erased from said optical disk.